A lamprey is a type of fish with a toothed, funnel-like, jawless sucking mouth with which it bores into the flesh of other fishes to suck their blood. In Zoology, Lampreys are not reckoned to be true fish because of the vastly different build of their body.

Lampreys live in coastal and freshwaters and are found in most temperate regions except Africa. Outwardly resembling eels in that they have no scales, an adult lamprey can range anywhere from 5 to 40 inches (13 to 100 centimetres) long. Lampreys have one or two dorsal fins, large eyes, one nostril on the top of their head, and seven gills on each side. A lamprey has cartilage instead of bones and is on the borderline between vertebrates and invertebrates. Lampreys begin life as burrowing, freshwater larvae (ammocoetes). At this stage, they are toothless, have rudimentary eyes, and feed on microorganisms. This larval stage can last five to seven years, and hence, was originally thought to be an idependent organism. After these five to seven years, they transform into adults and typically move into the sea to begin a parasitic life, attaching to a fish by their mouths and feeding on the blood and tissues of the host. To reproduce, lampreys return to freshwater, build a nest, then spawn, that is, lay their eggs, and die. Yet not all lampreys can be found in the sea. Some lampreys are landlocked and remain in freshwater, and some of these stop feeding altogether as soon as they have left the larval stage.

Lampreys have long been used as food for humans.

Recent studies reported in Nature suggest that lampreys have evolved a unique type of immune system with parts that are unrelated to the antibodies found in mammals.